This invention relates to improvements in steering column assemblies for vehicles.
It is known to provide a steering column assembly in which the steering shaft is adjustable for steering wheel height known as reach and for steering wheel distance known as rake. Such assemblies are known as double adjust steering columns. A steering column shroud is provided that supports the steering shaft that in turn supports the steering wheel. The shroud is in two parts, an upper part and a lower part, with the upper part telescoping over or into the lower part to permit the length of the shroud, and hence reach of the steering, to be adjusted. The lower part is secured to the vehicle at first point by a pivot and the upper part is secured to a fixed part of the vehicle at location nearer the steering wheel by a releasable clamp mechanism. When the clamp mechanism is clamped the upper and lower parts of the shroud are locked together. When released, the upper and lower parts of the shroud can move telescopically to enable reach to be adjusted. Also the whole shroud can be tilted up or down relative to the vehicle by pivoting around the pivot to provide rake adjustment.
The weight of the steering wheel and shaft and the shroud can be quite considerable, especially so where the column assembly also includes an electric motor and gearbox or a torque sensor, all of which are common parts of many electric power assisted steering assemblies. If the clamp mechanism is released and some additional support of the shroud is not present the steering wheel and shroud could fall down into a drivers lap with considerable force. Also, the weight of the assembly may inconvenience the driver when raising the wheel to the required position and securing the clamp mechanism. As the driver typically needs one hand free to operate the clamp this adjustment may prove burdensome.
To solve this problem it is common to provide a spring loaded support mechanism which acts between the vehicle and a part of the shroud. The spring mechanism takes some of the weight of the shroud and shaft and wheel when the clamp assembly is released for adjustment. This damps the fall of the assembly and assists the driver when they try to make rake adjustments by taking some of the weight.
In one known example of a possible prior art arrangement for a spring loaded support mechanism, the spring mechanism comprises a sling having a support bar that passes under the upper part of the shroud and which is connected at each end to a respective sprung arm. One arm is provided on each side of the shroud and connects an end of the arm to a fixed part of the vehicle body, usually above the shroud. Each arm comprises a coil spring or a leaf spring. In adjusting the assembly for reach, the base of the sling must slide over the lower surface of the upper person shroud as it moves relative to the lower portion. This movement can be quite stiff if friction is high and the operation may be noisy.